Duplex Color Scanning Technology

The newly developed compact scanning module for the rear side helps realize a high-speed color scanner equivalent in size to a conventional model while offering the same excellent imaging quality for both front and rear sides.

Duplex scanning for improved productivity

Heightened environmental awareness has spurred the shift to duplex printing, which halves paper consumption. Also, with more and more documents in color, there is an increasing need for high-speed color scanning.

This technology is for high-speed color scanning of sheets of paper on both sides. Because the conventional Auto Document Feeder (ADF) has only one scanning module, a document is mechanically reversed after scanning the front side in order to scan the rear side. Consequently, document scanning is time consuming.

By equipping the ADF with the newly developed compact, high-speed Contact Image Sensor (CIS) as the scanning module for the rear side (2nd scanning module), it has become possible to scan both front and rear sides with a single feed of a document. This results in a great improvement of scanning productivity and also leads to less damage to original documents and noise reduction.

Contact image sensor to achieve compact and thin scanning module

In order to keep the scanner about the same size as a conventional scanner, CIS, which can be miniaturized, is adopted as the scanning device for the rear side. As shown in the figure below, the front side is scanned by the first scanning module and the rear side is scanned by the second scanning module placed downstream of the document feeder.

Figure 1: Schematic drawing of document scanning module

As shown in Figure 2, in the case of CIS, a light source, a lens, and an image sensor are integrated and placed in almost direct contact with the document to be scanned. Because the imaging distance from the document to the image sensor is incredibly short, CIS realizes compact and thin scanning modules.

Scanning quality difference compensation technology

A CIS consists of multiple small image sensors aligned as shown in Figure 3.

Figure 3: Image sensor layout

Because of its structure, CIS raises issues, such as variation of color characteristics from one image sensor to another and missing pixels due to gaps between image sensors. To deal with these issues, Ricoh has developed new image processing technologies, namely, an image compensation technology for interpolation of missing pixels using peripheral pixels and a color compensation technology for compensation of color difference between the front side and the rear side.
Ricoh has loaded this image processing technologies to the custom LSI (Figure 4). As a result, imaging quality for front and rear sides is virtually identical despite the difference in the scanning system applied.